Historically, service providers have expended considerable effort to estimate equipment requirements, including how those requirements will change over time, in order to minimize cost while accommodating demand. Accurate estimation was important because over-estimating requirements could lead to over-provisioning with costly equipment. If, for example, a service provider estimates that for a given location there will be a requirement for equipment capable of throughput X for the first few years following introduction of a service, and that equipment capable of throughput 100X may be required within ten years, then it may not be economically rational to install the equipment capable of throughput 100X at service introduction. Rather, the service provider may wish to increase capacity gradually in relation to increased demand. However, there are practical limitations to gradually increasing capacity. First, each installation of new equipment has an overhead cost apart from that of the equipment itself, so it is desirable to reduce the frequency of new installations. Second, if increasing capacity requires that lower capacity equipment is replaced with higher capacity equipment then each capacity increase may produce excess equipment for which there may be no profitable use.
Scalable equipment mitigates some of the problems described above by facilitating gradual increases in capacity. One technique for creating a scalable switch is to use multiple I/O line cards interconnected via a backplane and switch fabric. The switch can then be scaled-up by adding line cards. Advantages of this technique include ease of installation and not producing excess equipment. However, the chassis which houses the fabric and line cards is typically of a size capable of accommodating a full complement of line cards. Hence, there is size inefficiency in a partially empty chassis. Such size inefficiency is a problem where space is costly. Size inefficiency is particularly problematic in markets where competing service providers co-locate equipment, and relatively newer providers rent space from incumbent service providers. It would therefore be desirable to have equipment that could scale gradually in physical size and capacity without producing excess equipment and without requiring complex installation.